This invention relates to a method of preparing poly(arylene ether ketones).
Poly(arylene ether ketones), in particular para-linked poly(arylene ether ketones), possess many desirable properties, for example, high temperature stability, mechanical strength, and resistance towards common solvents. The preparation of poly(arylene ether ketones) by two different approaches has been described in the literature. The first approach is an electrophilic synthesis in which an aryl ketone linkage is formed. The second approach is a nucleophilic synthesis in which an aryl ether linkage is formed.
In an electrophilic synthesis, the polymerization step involves the formation of an aryl ketone group derived from reaction the between an aromatic acid halide functional group and an activated hydrogen atom attached to an aromatic carbon atom, i.e., a hydrogen displaceable under the electrophilic reaction conditions. The monomer system employed in the polymerization can be, for example, (a) phosgene or an aromatic diacid dihalide and a polynuclear aromatic compound containing two activated hydrogen atoms, for example, terephthaloyl chloride and 1,4-diphenoxybenzene; or (b) a polynuclear aromatic compound containing both an acid halide group and an activated hydrogen atom, for example, p-phenoxybenzoyl chloride.
Electrophilic polymerizatons of this type are often referred to as Friedel-Crafts polymerizations. Typically, such polymerizations are carried out in a reaction medium comprising the reactant(s), a catalyst, such as anhydrous aluminum trichloride, and an inert solvent such as methylene chloride. Because the carbonyl groups of the reactant(s) and/or product(s) complex with aluminum trichloride and thereby deactivate it, the aluminum trichloride catalyst is generally employed in an amount slightly more than one equivalent for each equivalent of carbonyl groups in the reaction medium. Other metal halides such as ferric chloride may be employed as the catalyst. The preparation of poly(arylene ether ketones) by Friedel-Crafts polymerization is disclosed by Bonner, in U.S. Pat. No. 3,065,205; Berr, in U.S. Pat. No. 3,516,966; Jones, in U.S. Pat. No. 4,008,203; Goodman et al., in G.B. Pat. No. 971,227; and Jones, in G.B. Pat. No. 1,086,021.
The polymers as initially produced by these processes are generally relatively intractable and difficult to isolate and purify. Gander et al., in U.S. Pat. No. 3,791,380, address this problem and disclose a process which permits the preparation of polyketones in granular form. Their process comprises bringing into contact, in an organic medium, diphenyl ether and a stoichiometric amount of at least one compound selected from terephthalic and isophthalic acid chlorides with aluminum chloride catalyst and completing the reaction by abruptly dispersing the reaction mixture into a higher temperature fluid maintained at a temperature of about from 50.degree. C. to 130.degree. C., to effect an abrupt rise in temperature, the volume of said fluid being at least 200 percent of the initial volume of the reaction mixture, the reaction mixture being dispersed (a) prior to coagulation of the mixture and (b) after the elapse of at least 25 percent of the time period between the completion of the combination of reactants, including catalyst, and the coagulation of the reaction mixture. This process requires critical timing as the reaction mixture must be dispersed before gelation occurs. Further, the process subjects the reaction mixture to relatively high temperatures, thereby increasing the possibility of side reactions. The resulting product is granular and may entrap catalyst residues making purification more difficult.
Another solution to the problem of an intractable polymerization medium is the use of boron trifluoride catalyst in anhydrous hydrogen fluoride. See, for example, Marks, in U.S. Pat. No. 3,441,538; Thornton, in U.S. Pat. No. 3,442,857; Dahl, in U.S. Pat. No. 3,953,400; and Dahl et al., U.S. Pat. No. 3,956,240. The resulting polymer-catalyst complex is soluble in the hydrogen fluoride/boron trifluoride reaction medium. Recovery of the polymer from this reaction mixture and decomplexation of the polymer-catalyst complex while in solution are disclosed by Dahl in U.S. Pat. Nos. 3,751,398 and 4,239,884. However, the use of boron trifluoride and hydrogen fluoride requires special techniques and equipment making this process difficult to practice on a commercial scale.
Jansons et al., in U.S. Pat. No. 4,709,007 (1987) disclose an improved process for preparing poly(arylene ether ketones) in which a Lewis base controlling agent or, alternatively, a specified, exceptionally large excess of Lewis acid catalyst is used. This process, besides producing polymers of higher quality (higher molecular weight, with little or no ortho substitution), maintains the polymer in solution or in a more tractable state, facilitating its recovery and purification.
Yet another solution to the intractability problem is proposed by Reamey in U.S. Pat. No. 4,665,151. Reamey discloses that an intractable gel resulting from a Friedel-Crafts polymerization can be converted into a tractable gel or even a liquid reaction product by treatment with a liquefaction agent, such as anhydrous hydrogen chloride. However, Reamey's method has the disadvantage that additional material must be added to the polymerization mixture, requiring adaptation of the polymerization equipment with a means for introducing that material and a means for metering the requisite amount.
It would thus be desirable to be able to work up and isolate the poly(arylene ether ketone) product directly from a gelled Friedel-Crafts polymerization mixture without the need for the introduction of any additional components. The present invention provides such a method.